Parasites: eyeworm (loa loa)

The eyeworm (loa loa) is a parasite that is transmitted to humans by a fly bite, causing eyeworm disease. The worm enters the body and travels through the soft tissues in the body and can eventually end up in the eye. This African disease is also called Loiasis. What does this disease mean, how can you get it, what are the symptoms and what should you do to treat it?

How do you get eyeworm disease?

This eyeworm disease occurs in Central and West Africa and is also called loiasis . It is an infection caused by a parasite called Loa loa . The parasite is transmitted to humans by an infected fly (Chrysops fly) that bites a person. The fly can suck in an adult worm if it stings someone infected with eyeworm disease. The fly will develop larvae with which the fly will infect that person if it bites someone again. The adult worm moves through the soft tissues of the body and can end up in the eye.

The Chrysops fly

The Chrysops fly is a species of fly that occurs in the rainforest. Only the female flies will sting. They only sting humans, especially in the shade or in the house. They do this during the day and especially in the warmer months of the year. While sucking the blood, they release the loa larvae into the bloodstream. This is how a person becomes infected with this infection.


The first symptoms that occur after infection with eyeworm disease are hard, irritating and sometimes painless growths. It starts with itching, tingling, numbness or pain. These are called calabar swellings and can last for hours to weeks. If they occur in places in the body near joints, swelling can cause pain. The swelling is usually under the skin and sometimes there is only one swelling. The swelling usually occurs around the wrist and knee. However, it can also occur in other parts of the body, such as hands, forearms or legs. The calabar swelling is caused by a poison that an adult worm releases.


The disease can be diagnosed in the laboratory by microscopic examination. During the examination under the microscope, the worm larvae will be visible.


Once a diagnosis of eyeworm disease has been made, this infection will need to be treated with drugs such as diethylcarbamazine which will combat the worm larvae.


This disease is mainly caused during the warm months. Prevention is an important point. Infection can be prevented by avoiding places where many gadflies occur. In addition, protective clothing and insect repellents are recommended.

Health problem

This disease occurs almost exclusively in people in West and Central Africa. Outside this area it is a rare disease. Most of the population in this area is infected with eyeworm disease. This is a major social health problem. Travelers to this area also run a risk of becoming infected by a bite from the Chryops fly.

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